Trivial names sulfonic acids

Suitably substituted azo compounds constitute an important class of dyes—the azo dyes. Some derivatives such as /j-dimethylaminoazobenzene- p -sulfonic acid Na-salt (trivial name methyl orange) are used as pH-indicators. 

Diazotization of 3,7-diaminodibenzothiophene 5,5-dioxide, which has the trivial name of benzidine sulfone, followed by coupling with phenols, anilines, or arylsulfonic acids gives bis-azo dyes varying in color from red-brown to blue. These dyes are useful for the coloring of plastics and cellulose. second class of compounds based on 3,7-diamino-... 

Consensus on nomenclature had been reached by the 1890s. Aniline was the parent of its derivatives, though sulfonic acids were considered derivatives of benzene, such as aminobenzenesulfonic acid. The prefix amino- was added to naphthalene and its derivatives. Many trivial names came into use, particularly for aminonaphthalenesulfonic acids, found in both academic and industrial research laboratories. Though IUPAC convention now numbers amino aryl compounds according to the parent hydrocarbon, the earlier system of numbering has often been retained, since some names include the positions of substituents at carbon atoms numbered according to the older systems. 

Metanilic acid, the trivial name for m-aminobenzenesulfonic acid (aniline-3-sulfonic acid), is made by sulfonation of nitrobenzene, followed by B6champ reduction. It is used in reactive dyes and optical bleaching agents, or brighteners, that are added to detergents. 

Indolium cations are of conrse electrophilic species, in direct contrast with neutral indoles, and nnder favourable conditions will react as such. For example, the 3H-indolium cation itself will add bisnlhte at pH 4, under conditions that lead to the crystallisation of the product, the sodium salt of indoline-2-sulfonic acid (indoline is the widely used, trivial name for 2,3-dihydroindole). The salt reverts to indole on dissolution in water, however it can be M-acetylated and the resulting acetamide used for halogenation or nitration at C-5, final hydrolysis with loss of bisulfite affording the 5-substituted indole. ... 

---